Spain's security forces were on maximum alert Friday for the 50th anniversary of the armed Basque group ETA, blamed for bombings that killed two police officers and injured scores of people this week.

ETA was founded on July 31, 1959, and has killed more than 825 people since beginning its violent campaign for an independent Basque state in 1968.

Authorities blame ETA for two attacks this week — an explosion that killed two officers near a police barracks on Mallorca island Thursday and a car bomb that injured more than 60 people in the northern city of Burgos on Wednesday.

If confirmed as ETA attacks, the blasts would conflict with government assertions that the group is seriously weakened after major police crackdowns in Spain and France in recent years. Their timing, two days before the milestone anniversary, may be part of an ETA effort to demonstrate it is in no danger of breaking up.

"The government has given orders to the security forces to be on maximum alert, to double their work, to increase even more their efforts and to protect themselves from these vile murderers," Prime Minister Jose Luis Rodriguez Zapatero said late Thursday.

ETA is now blamed for nine attacks this year.

Authorities planned Friday to attend a funeral Mass on Mallorca for the two officers killed Thursday, who belonged to the paramilitary Civil Guard in charge of policing rural areas and guarding official buildings.

Several people were also injured lightly in Thursday's bombing in the Palmanova beach resort area, southwest of the island's capital, Palma de Mallorca.

The explosion, caused by a bomb attached to the underneath of a vehicle, occurred at the height of the summer holiday season for the Mediterranean island resort, which is one of Europe's main tourist destinations.

Television images showed the charred and mangled remains of a vehicle parked near the police barracks. Officials shut down the island's airports and ports for several hours while police searched for bombing suspects.

Police believe the attack was carried out by an ETA cell that came to the island specifically to carry it out and was not based there, Interior Ministry official Ramon Socias said.

The attack Wednesday morning on the Spanish mainland also targeted a police compound and surrounding buildings, in which around 120 people including dozens of children were at the time of the blast. More than 60 people were reported injured.

There were no warning calls before the two attacks, for which no group has claimed responsibility.

Zapatero said the attacks were staged as Spanish police in collaboration with French counterparts were hitting ETA hard "dismantling its organization, thwarting its action, identifying its members and detaining them more rapidly each time and in greater numbers."

Spain has vowed to crush the separatist group since ETA ended what it had said was a permanent cease-fire with a 2006 bombing that destroyed a Madrid airport parking garage and killed two people.